Blast furnaces have been used to chemically reduce and physically convert iron oxides into liquid iron. Often, the blast furnace includes a large steel stack lined with refractory brick, where iron ore, coke, and limestone are dumped into the top, and preheated air is blown into the bottom. These materials descend to the bottom of the furnace where they become the final product of liquid slag and liquid iron, which are normally drained from the furnace at regular intervals. Once a blast furnace has been started, it can continuously run for years.
The cupola plasma furnace functions similarly to a blast furnace, except that it makes molten cast iron from scrap steel or scrap substitutes. The fuel for this furnace is usually coke and often requires megawatts of plasma power. During operation, heated air is boosted in temperature with a plasma torch and blown into the bottom of the cupola. The coke can be burned creating more heat, which melts the iron. The iron can then exit the furnace and run through a trough to an iron ladle.
It is known that a plasma can be ignited by subjecting a gas to a sufficient amount of microwave radiation at reduced pressure. Vacuum equipment, however, can be expensive, slow, and energy-consuming. Moreover, the use of such equipment can limit the applications of such furnaces.